The following question refers to the figure of a family's pedigree chart, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle.

What is the likelihood that a future child of IV-3 and IV-4 will have the trait?

Question

The following question refers to the figure of a family's pedigree chart, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle.

What is the likelihood that a future child of IV-3 and IV-4 will have the trait?

BlackTom AI · Accepted Answer

The question asks about the likelihood that a future child of IV-3 and IV-4 will have the dominant trait W, given the pedigree.
Option analysis:
- 0%: If both IV-3 and IV-4 are unaffected individuals in a family where W is dominant, each unaffected person must have genotype ww (no W allele). When two ww individuals mate, every child must inherit a w allele from each parent, resulting in ww for all offspring. Therefore, the chance of their child being affected (having W) is 0%. This reasoning hinges on the assumption from the pedigree that IV-3 and IV-4 are not expressing the W phenotype.
- 25%: This would be the typical Mendelian risk for a cross between two heterozygotes (Ww x Ww) producing offspring with genotype WW, Ww, or ww in a 1:2:1 ratio. However, this requires both parents to be carriers (Ww). If either parent is ww (unaffected with no W allele), a 25% risk would not apply because ww cannot contribute a W allele.
- 75%: This option is not consistent with standard inheritance patterns for a single dominant allele. A 75% risk would imply that three of four possible outcomes involve the trait, which doesn’t align with simple dominant-recessive inheritance across a single locus unless additional complexities (e.g., incomplete penetrance, multiple genes, or data misinterpretation) are specified, which are not present in the given pedigree.
- 50%: A 50% risk is characteristic of a cross where exactly one parent is heterozygous (Ww) and the other is homozygous recessive (ww). In that case, each child has a 50% chance of inheriting W. However, this requires one parent to be heterozygous and the other to be ww, which contradicts our conclusion that both IV-3 and IV-4 are unaffected and thus ww. Without evidence that one parent carries W while the other does not, this option is unlikely.
- 100%: A 100% risk would occur if both parents were homozygous dominant (WW) or if the trait were obligate in all offspring due to a fixed genotype. The pedigree does not indicate that both IV-3 and IV-4 are WW; moreover, an unaffected pair cannot produce all affected offspring under a simple dominant model. Therefore, this option does not fit the given information.
In summary, given that IV-3 and IV-4 are shown as unaffected in the pedigree, they must both be ww genotypes, and their child must also be ww, yielding 0% probability of the child being affected.

W25 BIOL D006B 01Y Cell & Molecular Biology Lecture Exam 3

The following question refers to the figure of a family's pedigree chart, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle. What is the likelihood that a future child of IV-3 and IV-4 will have the trait?

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